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From: rxin <git@git.apache.org>
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Subject: [GitHub] spark pull request #14116: [SPARK-16452][SQL] Support basic
 INFORMATION_SCHE...
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Message-Id: <20160711201112.1039CDFFF8@git1-us-west.apache.org>
Date: Mon, 11 Jul 2016 20:11:12 +0000 (UTC)

Github user rxin commented on a diff in the pull request:

    https://github.com/apache/spark/pull/14116#discussion_r70327368
  
    --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/systemcatalog/InformationSchema.scala ---
    @@ -0,0 +1,336 @@
    +/*
    + * Licensed to the Apache Software Foundation (ASF) under one or more
    + * contributor license agreements.  See the NOTICE file distributed with
    + * this work for additional information regarding copyright ownership.
    + * The ASF licenses this file to You under the Apache License, Version 2.0
    + * (the "License"); you may not use this file except in compliance with
    + * the License.  You may obtain a copy of the License at
    + *
    + *    http://www.apache.org/licenses/LICENSE-2.0
    + *
    + * Unless required by applicable law or agreed to in writing, software
    + * distributed under the License is distributed on an "AS IS" BASIS,
    + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    + * See the License for the specific language governing permissions and
    + * limitations under the License.
    + */
    +
    +package org.apache.spark.sql.execution.systemcatalog
    +
    +import java.sql.{Date, Timestamp}
    +
    +import scala.collection.mutable.ArrayBuffer
    +
    +import org.apache.commons.lang3.StringUtils
    +
    +import org.apache.spark.rdd.RDD
    +import org.apache.spark.sql._
    +import org.apache.spark.sql.catalyst.dsl.plans._
    +import org.apache.spark.sql.catalyst.expressions.Alias
    +import org.apache.spark.sql.catalyst.plans.logical.Project
    +import org.apache.spark.sql.execution.datasources._
    +import org.apache.spark.sql.sources._
    +import org.apache.spark.sql.types._
    +
    +/**
    + * INFORMATION_SCHEMA is a database consisting views which provide information about all of the
    + * tables, views, columns in a database.
    + */
    +object InformationSchema {
    +  val INFORMATION_SCHEMA = "information_schema"
    +  /**
    +   * Register INFORMATION_SCHEMA database.
    +   */
    +  def registerInformationSchema(sparkSession: SparkSession): Unit = {
    +    sparkSession.sql(s"CREATE DATABASE IF NOT EXISTS $INFORMATION_SCHEMA")
    +    registerView(sparkSession, new DatabasesRelationProvider, Seq("schemata", "databases"))
    +    registerView(sparkSession, new TablesRelationProvider, Seq("tables"))
    +    registerView(sparkSession, new ViewsRelationProvider, Seq("views"))
    +    registerView(sparkSession, new ColumnsRelationProvider, Seq("columns"))
    +    registerView(sparkSession, new SessionVariablesRelationProvider, Seq("session_variables"))
    +  }
    +
    +  /**
    +   * Register a INFORMATION_SCHEMA relation provider as a temporary view of Spark Catalog.
    +   */
    +  private def registerView(
    +      sparkSession: SparkSession,
    +      relationProvider: SchemaRelationProvider,
    +      names: Seq[String]) {
    +    val plan =
    +      LogicalRelation(relationProvider.createRelation(sparkSession.sqlContext, null, null)).analyze
    +    val projectList = plan.output.zip(plan.schema).map {
    +      case (attr, col) => Alias(attr, col.name)()
    +    }
    +    sparkSession.sessionState.executePlan(Project(projectList, plan))
    +    for (name <- names) {
    +      // TODO(dongjoon): This is a hack to give a database concept for Spark temporary views.
    +      // We should generalize this later.
    +      sparkSession.sessionState.catalog.createTempView(s"$INFORMATION_SCHEMA.$name",
    +        plan, overrideIfExists = true)
    +    }
    +  }
    +
    +  /**
    +   * Compile filter array into single string condition.
    +   */
    +  private[systemcatalog] def getConditionExpressionString(filters: Array[Filter]): String = {
    +    val str = filters.flatMap(InformationSchema.compileFilter).map(p => s"($p)").mkString(" AND ")
    +    if (str.length == 0) "TRUE" else str
    +  }
    +
    +  /**
    +   * Convert filter into string expression.
    +   */
    +  private[systemcatalog] def compileFilter(f: Filter): Option[String] = {
    --- End diff --
    
    it might make it easier to implement catalystscan


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